As it is known, a radio access network provides voice services (calls, conference calls) and/or data services (text message delivery, image delivery, IP data connections, etc.) to users provided with respective mobile terminals, such as for instance mobile phones, PDAs, PCs provided with mobile interfaces, and so on.
A radio access network typically comprises a number of nodes (in particular, base stations, relay nodes, repeaters and remote radio heads) spread over a geographical area.
Each base station is suitable for exchanging traffic over one or more RF (Radio Frequency) carriers with mobile terminals located in its coverage area (or “cell”). In particular, each base station collects traffic generated by the mobile terminals located in its cell and forwards it in the upstream direction towards a core network. On the other hand, each base station receives traffic in the downstream direction from the core network and distributes it to mobile terminals located in its cell. Different types of base stations are known, for instance: macro base stations covering macrocells (i.e. very wide cells which are typically found in rural areas or along highways, as well as the so-called “umbrella cells” in urban environments), micro base stations covering microcells (i.e. smaller cells typical of densely populated urban areas), pico base stations covering picocells (very small cells which may be found e.g. in a large office, a mall or a train station), femto base stations covering femtocells (the cells with the smallest area, which ca be provided e.g. in homes or small offices).
On the other hand, relay nodes and repeaters are nodes responsible for conveying the RF signals exchanged between base stations and mobile terminals, which may be used when an increased RF power is needed (e.g. when the interference between RF carriers is particularly high or at the edges of the cells). Relay nodes for LTE-Advanced, as defined in 3GPP, are part of the radio access network and operate, from a UE (User Equipment) perspective, like an eNB (evolved NodeB). A relay node for LTE-Advanced network is a node wirelessly connected to a donor eNB.
On the other hand, remote radio heads (also briefly termed RRHs) can convey the RF signal of a node via fiber optic cables extending the coverage of a node to remote locations.
The nodes of a radio access network may also be equipped with active antennas (which are fed by optical fiber), enabling significant power savings in both the base station and the user equipments.
In a homogeneous radio access network, all the nodes are based on a same radio access technology. Exemplary radio access technologies are: GSM (Global System for Mobile communication), UMTS (Universal Mobile Telecommunication System) and LTE (Long Term Evolution).
A heterogeneous radio access network may instead comprise nodes based on different radio access technologies and/or nodes of different types (macro base stations, micro base stations, relay nodes, repeaters, remote radio heads, etc.) within a same radio access technology. Further, a heterogeneous access network may comprise one or more multistandard base stations, i.e. base stations combining different radio access technologies in a single hardware which may be configured via software to operate according to any of such radio access technologies.
Nodes based on different radio access technologies may be located at a same geographical position (i.e. they may be co-located). For instance, a same site may comprise both a GSM BTS (Base Transceiver Station) and a multistandard base station configured to operate as a UMTS NodeB or an LTE eNodeB. Otherwise, nodes based on different radio access technologies may be located at different geographical positions. In any case, cells covered by nodes based on different radio access technologies may at least partially overlap. In that case, according to its current position and to its capabilities, a mobile terminal may use any of the available radio access technologies for accessing a service delivered by the radio access network, provided that the selected technology is capable of supporting delivery of that service with a suitable Quality of Service.
In a radio communication system comprising a radio access network, the power consumption is due for the most part (70%-80%) to the radio access network and, in particular, to the base stations. Indeed, although the power consumption of a single base station is quite contained (500 W to 3 kW, according to the technology and to the base station type), a radio access network typically comprises a very high number of base stations.
Hence, in view of reducing the environmental impact of radio communication systems, designing radio access networks with reduced power consumption and/or operating a radio access network so as to minimize its power consumption is a key point.
“Energy-aware UMTS access networks” by L. Chiaravaglio et al., The 11th International Symposium on Wireless Personal Multimedia Communication (WPMC'08), Sep. 8-11, 2008, Lapland (Finland) discloses to reduce, based on traffic intensity, the number of active access devices when they are under-utilised, such as during night periods. When some base transceiver stations are switched off, radio coverage and service provisioning are taken care of by the devices that remain active. The switch off of the access devices should be decided so as to maintain quality of service guarantees and meet electromagnetic exposure constraints.
WO 2002/07464 describes to measure the traffic load of a node and use it for determining whether or not the node enters a power saving mode by turning off certain components or functions of the node and/or by instructing certain components or function of the node to enter a sleep mode, e.g.: switching off or putting to sleep one or more MCPAs (Multi Carrier Power Amplifier); turning off one or more carriers; turning off one or more selectors with regards to a frequency; turning off or putting to sleep one or more circuit boards or parts of boards; and/or reducing fan speed based upon traffic load of the node.